Revert "Update for changes to TraitItem on master."

This reverts commit 1d23be75b95b1dad318020fcf110836a7f17fc80.

Author: nikomatsakis

src/librustc/infer/error_reporting.rs

@@ -116,9 +116,9 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 
         fn trait_item_scope_tag(item: &hir::TraitItem) -> &'static str {
             match item.node {
-                hir::TraitItemKind::Method(..) => "method body",
-                hir::TraitItemKind::Const(..) |
-                hir::TraitItemKind::Type(..) => "associated item"
+                hir::MethodTraitItem(..) => "method body",
+                hir::ConstTraitItem(..) |
+                hir::TypeTraitItem(..) => "associated item"
             }
         }